An electrophotographic image forming apparatus may be provided with a cartridge including a developing device. The cartridge is configured to be detachably attached to a body of the image forming apparatus. The cartridge includes a case storing toner as a developing agent and a developing roller rotatably mounted to the inside of an opening formed in the case. The developing roller is designed to form a visible image by transferring a thin toner layer formed on the developing roller to an electrostatic latent image formed on a photosensitive member drum. A toner leak prevention member, or a side seal, is attached to the case. The side seal contacts a circumferential surface of the developing roller at each end to prevent toner leakage. However, even when the side seal is mounted to the cartridge, toner may leak from both ends of the developing roller, causing a toner stain on the inside of the apparatus or on an operator's fingers or clothing during cartridge replacement.
Japanese Laid-Open Patent Publication No. 2001-60040 proposes a cartridge where a film prevention member is affixed to an end portion of a bottom wall of a cartridge case extending sideways at a lower portion of an opening to prevent toner that leaks on the bottom wall from flowing from the end portion to outside the cartridge case.
The above structure is applied to a cartridge that is attached to the apparatus body in a position where the opening is horizontally oriented. The position of the cartridge is not changed between when it is mounted to the apparatus body and placed on a horizontal surface such as a desktop. However, when there is a change in the position of the cartridge between when it is mounted to the apparatus body and placed on the horizontal surface, for example, when the cartridge is attached to the apparatus body in a position where the opening faces downward, the above structure may not be capable of preventing toner from leaking outside.